First Calorimetric Measurement of OI-line in the Electron Capture Spectrum of 163^{163}Ho

The isotope $^{163}$Ho undergoes an electron capture process with a recommended value for the energy available to the decay, $Q_{\rm EC}$, of about 2.5 keV. According to the present knowledge, this is the lowest $Q_{\rm EC}$ value for electron capture processes. Because of that, $^{163}$Ho is the best candidate to perform experiments to investigate the value of the electron neutrino mass based on the analysis of the calorimetrically measured spectrum. We present for the first time the calorimetric measurement of the atomic de-excitation of the $^{163}$Dy daughter atom upon the capture of an electron from the 5s shell in $^{163}$Ho, OI-line. The measured peak energy is 48 eV. This measurement was performed using low temperature metallic magnetic calorimeters with the $^{163}$Ho ion implanted in the absorber. We demonstrate that the calorimetric spectrum of $^{163}$Ho can be measured with high precision and that the parameters describing the spectrum can be learned from the analysis of the data. Finally, we discuss the implications of this result for the Electron Capture $^{163}$Ho experiment, ECHo, aiming to reach sub-eV sensitivity on the electron neutrino mass by a high precision and high statistics calorimetric measurement of the $^{163}$Ho spectrum.Comment: 5 pages, 3 figure

Development and characterization of metallic magnetic calorimeters for the calorimetric measurement of the electron capture spectrum of 163Ho for the purpose of neutrino mass determination

The electron capture process of 163Ho offers a unique tool for the determination of the neutrino mass due to its low end-point energy Q_EC. In this work a metallic magnetic calorimeter with an embedded 163Ho source was characterized and used to measure the calorimetric spectrum of the 163Ho decay. The characterization revealed that neither the thermodynamic properties nor the detector performance were impaired by the presence or the ion-implantation process of the 163Ho source. Furthermore an energy resolution of Delta E_FWHM = 7.3 eV and rise times as low as tau_0 = 80 ns were measured. The discussed detector achieved the presently best energy resolution for the measurement of the 163Ho electron capture spectrum. For the first time the de-excitation of an electron capture from the 163Ho O1-level at E_O1 = 48eV has been observed. The parameters describing the spectrum could be extracted from the measured spectra. One of the most important parameters, namely the end-point energy has been determined to Q_EC = (2.877 ± 0.022 (stat.) +0 - 0.06 (syst.)) keV. This implies that the achieved detector performance is suited for a neutrino mass experiment based on 163Ho

Improved Source/Absorber Preparation for Radionuclide Spectrometry Based on Low-Temperature Calorimetric Detectors

High-resolution beta spectrometry based on low-temperature calorimetric detectors requires high-quality source/absorber combinations in order to avoid spectrum artifacts and to achieve optimal detection efficiency. In this work, preparation techniques and quality control methods to fabricate reliable source/absorber assemblies with the radionuclide under investigation embedded into them are discussed. © 2019, The Author(s)

A pulsed, mono-energetic and angular-selective UV photo-electron source for the commissioning of the KATRIN experiment

The KATRIN experiment aims to determine the neutrino mass scale with a sensitivity of 200 meV/c^2 (90% C.L.) by a precision measurement of the shape of the tritium $\beta$-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. To determine the transmission properties of the KATRIN main spectrometer, a mono-energetic and angular-selective electron source has been developed. In preparation for the second commissioning phase of the main spectrometer, a measurement phase was carried out at the KATRIN monitor spectrometer where the device was operated in a MAC-E filter setup for testing. The results of these measurements are compared with simulations using the particle-tracking software "Kassiopeia", which was developed in the KATRIN collaboration over recent years.Comment: 19 pages, 16 figures, submitted to European Physical Journal

A pulsed, mono-energetic and angular-selective UV photo-electron source for the commissioning of the KATRIN experiment

The KATRIN experiment aims to determine the neutrino mass scale with a sensitivity of 200 ${\mathrm{meV}/\mathrm{c}^2}$ (90% C. L.) by a precision measurement of the shape of the tritium $\beta$-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. To determine the transmission properties of the KATRIN main spectrometer, a mono-energetic and angular-selective electron source has been developed. In preparation for the second commissioning phase of the main spectrometer, a measurement phase was carried out at the KATRIN monitor spectrometer where the device was operated in a MAC-E filter setup for testing. The results of these measurements are compared with simulations using the particle-tracking software “Kassiopeia”, which was developed in the KATRIN collaboration over recent years

Characterization of the 163^{163}Ho Electron Capture Spectrum: A Step Towards the Electron Neutrino Mass Determination

The isotope $^{163}$Ho is in many ways the best candidate to perform experiments to investigate the value of the electron neutrino mass. It undergoes an electron capture process to $^{163}$Dy with an energy available to the decay, Q$_{EC}$, of about 2.8 keV. According to the present knowledge, this is the lowest Q$_{EC}$ value for such transitions. Here we discuss a newly obtained spectrum of $^{163}$Ho, taken by cryogenic metallic magnetic calorimeters with $^{163}$Ho implanted in the absorbers and operated in anticoincident mode for background reduction. For the first time, the atomic deexcitation of the $^{163}$Dy daughter atom following the capture of electrons from the 5s shell in $^{163}$Ho, the OI line, was observed with a calorimetric measurement. The peak energy is determined to be 48 eV. In addition, a precise determination of the energy available for the decay Q$_{EC}$=(2.858±0.010$_{stat}$±0.05$_{syst}$)  keV was obtained by analyzing the intensities of the lines in the spectrum. This value is in good agreement with the measurement of the mass difference between $^{163}$Ho and $^{163}$Dy obtained by Penning-trap mass spectrometry, demonstrating the reliability of the calorimetric technique

MetroMMC: Electron-Capture Spectrometry with Cryogenic Calorimeters for Science and Technology

Accurate decay data of radionuclides are necessary for many fields of science and technology, ranging from medicine and particle physics to metrology. However, data that are in use today are mostly based on measurements or theoretical calculation methods that are rather old. Recent measurements with cryogenic detectors and other methods show significant discrepancies to both older experimental data and theory in some cases. Moreover, the old results often suffer from large or underestimated uncertainties. This is in particular the case for electron-capture (EC) decays, where only a few selected radionuclides have ever been measured. To systematically address these shortcomings, the European metrology project MetroMMC aims at investigating six radionuclides decaying by EC. The nuclides are chosen to cover a wide range of atomic numbers Z, which results in a wide range of decay energies and includes different decay modes, such as pure EC or EC accompanied by γ- and/or β+-transitions. These will be measured using metallic magnetic calorimeters (MMCs), cryogenic energy-dispersive detectors with high-energy resolution, low-energy threshold and high, adjustable stopping power that are well suited for measurements of the total decay energy and X-ray spectrometry. Within the MetroMMC project, these detectors are used to obtain X-ray emission intensities of external sources as well as fractional EC probabilities of sources embedded in a 4 π absorber. Experimentally determined nuclear and atomic data will be compared to state-of-the-art theoretical calculations which will be further developed within the project. This contribution introduces the MetroMMC project and in particular its experimental approach. The challenges in EC spectrometry are to adapt the detectors and the source preparation to the different decay channels and the wide energy range involved, while keeping the good resolution and especially the low-energy threshold to measure the EC from outer shells. © 2019, The Author(s)

keV-Scale sterile neutrino sensitivity estimation with time-of-flight spectroscopy in KATRIN using self-consistent approximate Monte Carlo

We investigate the sensitivity of the Karlsruhe Tritium Neutrino Experiment (KATRIN) to keV-scale sterile neutrinos, which are promising dark matter candidates. Since the active-sterile mixing would lead to a second component in the tritium β β -spectrum with a weak relative intensity of order sin 2 θ≲10 −6 sin2⁡θ≲10−6 , additional experimental strategies are required to extract this small signature and to eliminate systematics. A possible strategy is to run the experiment in an alternative time-of-flight (TOF) mode, yielding differential TOF spectra in contrast to the integrating standard mode. In order to estimate the sensitivity from a reduced sample size, a new analysis method, called self-consistent approximate Monte Carlo (SCAMC), has been developed. The simulations show that an ideal TOF mode would be able to achieve a statistical sensitivity of sin 2 θ∼5×10 −9 sin2⁡θ∼5×10−9 at one σ σ , improving the standard mode by approximately a factor two. This relative benefit grows significantly if additional exemplary systematics are considered. A possible implementation of the TOF mode with existing hardware, called gated filtering, is investigated, which, however, comes at the price of a reduced average signal rate

Characterization of low temperature metallic magnetic calorimeters having gold absorbers with implanted 163^{163}Ho ions

For the first time we have investigated the behavior of fully micro-fabricated low temperature metallic magnetic calorimeters (MMCs) after undergoing an ion-implantation process. This experiment had the aim to show the possibility to perform a high precision calorimetric measurement of the energy spectrum following the electron capture of $^{163}$Ho using MMCs having the radioactive $^{163}$Ho ions implanted in the absorber. The implantation of $^{163}$Ho ions was performed at ISOLDE-CERN. The performance of a detector that underwent an ion-implantation process is compared to the one of a detector without implanted ions. The results show that the implantation dose of ions used in this experiment does not compromise the properties of the detector. In addition an optimized detector design for future $^{163}$Ho experiments is presented